DE69114170T2 - Error correction for color filters. - Google Patents

Description

The present invention relates to the correction of errors in color filters and, more particularly, to a method for correcting pixel errors in color filters suitable for use in a liquid crystal display device.

There are many methods for producing color filters used in color liquid crystal displays, such as the dyeing method, the electrodeposition method, the printing method and the dispersion method. In the dyeing method, a synthetic high polymer or a natural protein such as gelatin, glue or casein is dyed to obtain a color filter. However, the color filter produced by this method has problems in storage stability with respect to moisture, light resistance and heat resistance; in larger images, it is difficult to achieve uniform control of the dyeing and adhesive characteristics, resulting in problems in controlling both the film thickness and uniform color distribution.

In the electroplating process, a voltage is applied to a transparent electrode, which has been previously prepared in a specific shape, while it is in a bath of an ionized high polymer. This polymer contains a pigment dissolved or finely dispersed in a solvent to color the pixels. In the electroplating process, a photolithographic process, including coating the transparent electrode to form the color filters, and a coating layer connected to the transparent electrode are used. For color filters made by this method, any short circuit will cause a conduction failure, which will result in a drop in performance. Therefore, there are problems because it is difficult to apply the method and control the quality of the transparent electrode film.

The printing process uses methods such as dry offset printing and offset gravure printing. However, the use of this method is limited because filtering the ink is difficult due to its high viscosity, defects tend to occur frequently due to dust, foreign matter and ink binding gel, and there are problems with insufficient positioning accuracy, row width accuracy and surface smoothness. For these reasons, it is difficult to apply the method to large-screen high-resolution color displays.

The dispersion method produces color filters in which pigments are finely dispersed in a photosensitive negative resin. The dispersion method forms colored pixels through a coating, exposure and development process. The filter produced by this method is resistant to stresses such as light and heat because pigments are used. In addition, the positioning accuracy is adequate because the pattern is applied using photolithography. Therefore, this method is suitable for high-resolution color displays with a large screen.

Published Unexamined Patent Application (PUPA) 63-128302 discloses a method in which colored pixels are formed by the printing process and then pinhole errors are corrected, and in which a black matrix is formed by exposing a black negative photosensitive resin applied to the colored pixels from the side of the transparent substrate, using the colored pixels as a photomask. The paper entitled "Self-Alignment Fabrication of ITO Electrode Pattern on Electrodeposited Tricolour Filter in Black Matrix: An Application to STN-LCD" by T. Fukuchi, M. Suginoya, H. Kawamon and K. Iwasa, published on pages 388 to 391 of "JAPAN DISPLAY '89", issue of October 16, 1989, discloses the fabrication of a black matrix between coloured pixels formed by electrodeposition. The method comprises applying a black negative photosensitive resin to the entire surface of the transparent substrate side (after forming coloured pixels by electrodeposition) and then exposing this resin using the coloured pixels as a photomask.

According to the method of PUPA 63-128302, the black matrix area and the pinhole areas of the colored pixels have the same optical density because the black matrix and the pinhole areas of the colored pixels are made of and filled with the black resin of identical material with identical film thickness. Since the black matrix requires an optical density of at least 2.0 (log 1/T, where T is the light transmittance) for light shielding, the pinhole areas can be regarded as black defects, especially when a static image is displayed.

In the paper by Fukuchi et al. (JAPAN DISPLAY, 1989), only a method is proposed to produce a black self-aligning matrix, but nowhere is it suggested how to correct the defects in the color filter. When there are pinhole defects caused by the photolithographic process or the process of filter manufacture by electroplating, the pinhole defects are filled with a black resin having the same optical density as the black matrix, and they can be regarded as a black defect, especially when a static image is displayed, as in the case of PUPA 63-128302. Therefore, the method of repairing the defective area and Simultaneously producing the black matrix with the same material only results in white defects becoming black defects, which nevertheless still appear as defects when displayed; therefore, this cannot be considered a true repair.

It is a primary object of the invention to provide a simple method for correcting errors in a color filter containing colored pixels so that the errors produced in the filter are not recognized as errors in normal use when characters or graphics are displayed through the color filter.

A second object of the invention is to provide a simple method of repairing a color filter so that even a defect extending over several colored pixels is not recognized as a defect in normal use when characters or graphics are displayed through the filter.

From a first aspect, the present invention provides a method of correcting defects in a color filter containing colored pixels, the colored pixels being formed from a photosensitive negative resin containing a pigment, the defect or defects affecting only pixels of a single particular color, the method comprising the steps of:

for applying a photosensitive, negative repair resin in which a pigment of the color in which the colored pixels have the defect is distributed, to the colored pixels having the defect; for exposing the applied repair resin to light through the colored pixels having the defect, the light having a wavelength at which the repair resin reacts, but at which the light transmittance of the colored pixels is low, so that the repair resin reacts only in the defective area; and for developing the exposed repair resin, leaving only the part of the repair resin that reacted.

Viewed from a second aspect, the present invention provides a method of correcting defects in a color filter containing colored pixels, the colored pixels being formed from a photosensitive negative resin containing a pigment, the defect extending over a plurality of pixels of different colors, the method comprising the steps of: applying a photosensitive negative repair resin colored gray with a pigment to the plurality of colored pixels having the defect; exposing the applied repair resin to light through the plurality of colored pixels having the defect, the light having a wavelength at which the repair resin reacts, but at which the transmittance of the colored pixels is low, so that the repair resin reacts only in the defect area; and developing the exposed repair resin, leaving only the portion of the repair resin that reacted.

Color filters having defective pixels repaired by the method of the present invention can be used in the same manner as filters without defects. In preferred embodiments, the corrected color filters can be incorporated into a liquid crystal display device having a liquid crystal layer sandwiched between a pair of transparent substrates.

The present invention will now be described in more detail by way of example and with reference to an embodiment thereof, as shown in the accompanying drawings, in which

Figure 1 is a sectional view showing the three steps during the correction process according to the preferred embodiment of the present invention;

Figure 2 is a plan view showing a color filter having an error in its color pixels for which the correction method shown in Figure 1 is intended ;

Figure 3 shows a cross-section along the line A-A of Figure 2 ;

Figure 4 is a spectral diagram showing the emission spectrum of the light source used in the exposure process of the correction method shown in Figure 1;

Figure 5 is a spectral diagram showing the spectral transmission spectrum of the defective red, green and blue pixels of the color filter serving as a photomask in the exposure process of the correction method shown in Figure 1;

Figure 6 is a diagram showing the spectral sensitivity of the negative photosensitive resin containing a pigment and used as a repair material;

Figure 7 is a plan view showing a color filter having a defect extending across multiple colored pixels of different colors;

Figure 8 shows a section along the line B-B of Figure 7 ;

Figure 9 is a cross-section showing three steps of a preferred method for correcting an error extending across colored pixels of different colors; and

Figure 10 is a cross-sectional view showing an example of a liquid crystal display device in which a color filter which has been corrected using the method of the preferred embodiment shown in Figure 1.

Figure 1 shows the individual steps of the process for correcting a color filter according to the preferred embodiment of the invention. Figures 2 and 3 show a color filter with a defect to which the correction method shown in Figure 1 is applied. In Figures 2 and 3, the red pixels 1R, the green pixels 1G and the blue pixels 1B are arranged on a transparent substrate 4 made of glass. The red, green and blue pixels 1R, 1G and 1B are made of a photosensitive negative resin each containing pigments of the corresponding colors. Hereinafter, the term "colored pixel" is used as a general term that includes the red, green and blue pixels. Between the colored pixels, a black matrix 2 is provided for light shielding. The black matrix 2 can be formed from a metal, such as chromium, or an organic film with a finely distributed material (pigment, dye) of black color.

When a defect 3, such as a pinhole or a break, is present in a colored pixel, light generated by a light source behind it passes directly through the defect 3 and creates an area of different brightness in the area of the colored pixels. This is easily detected, especially when a static image is displayed. In the preferred embodiment, the defective area is corrected by filling it with a negative photosensitive resin containing a pigment of the same color as the material forming the colored pixel.

When light is transmitted from the side of the substrate 4, the intensity and spectrum of the light transmitted through the defective area 3 will naturally differ from the intensity and spectrum of the light transmitted through the area of a properly manufactured color filter. the light in the defective region 3 is transmitted only through the glass substrate 4, the intensity and spectrum of the light are not significantly changed, whereas in the regions formed by the colored pixels 1R, 1G and 1B, the light is attenuated by the amount of light absorbed by the colored pixels, and therefore the intensity and spectrum differ considerably from the intensity and spectrum of the light transmitted through the defective region 3.

Figure 4 shows an emission spectrum of the high voltage mercury vapor lamp used in the correction process, while Figure 5 shows a spectrum of the spectral transmittance of properly prepared red, green and blue colored pixels used as a photomask, and Figure 6 shows the relative spectral sensitivity of the photosensitive negative repair resin with the pigment dispersed therein. In Figure 6, BKm B, G and R represent the relative spectral sensitivity of the photosensitive negative repair resins containing black, blue, green and red pigments, respectively. From Figure 6, it is clear that the photosensitive negative repair resin with the pigment dispersed therein responds mainly to light of line i (365 nm) in forming patterns, and from Figure 5, it is clear that the transmittance at 365 nm is 7.6% for red pixels, 0.89% for green pixels and 0.01% for blue pixels. When the photosensitive, negative repair resin 5 with the pigment finely distributed therein is applied to the pixels shown in Figure 1 (a) and when light 6 is irradiated from the side of the transparent substrate 4 through the colored pixels 1B, 1R and 1G, as shown in Figure 1 (b), the photosensitive, negative repair resin reacts and polymerizes in the defective area 3. However, on the colored pixels 1B, 1R and 1G, the photosensitive, negative repair resin does not react due to the mask effect of the colored pixels and is removed during development. Accordingly, the defective area is automatically aligned with the Repair material 5 is filled as shown in Figure 1 (c).

A negative photosensitive resin that satisfies the above conditions is, for example, a radical polymerization photosensitive resin in which pigments of various colors with submicroscopic particle diameters are dispersed, as described in PUPA 1-152449. This photosensitive resin contains a polyfunctional acrylic ester monomer, a trihalomethyltriazine type photopolymerization initiator, and an acrylic acid/acrylic ester copolymer.

The color pigments with submicroscopic particle diameter have the same composition as each type of the already formed colored pixels. In particular, the red pigment contains at least one anthraquinone type pigment and one perylene type pigment mixed with one isomdoline type yellow pigment or one disazo type yellow pigment. The green pigment contains a phthalocyanine type halogenated pigment mixed with one disazo type yellow pigment or one isomdoline type yellow pigment, and the blue pigment contains a phthalocyanine type pigment mixed with one dioxazine type violet pigment.

Figures 7 and 8 show a color filter having a defect extending over several pixels of different colors. The presence of a defective area 13 extending over neighboring pixels of different colors is easily recognized as a defect, since the brightness of the defective area 13 differs from the brightness of the area formed by the colored pixels, resulting in a significantly poorer display quality. If such a defective area is filled with a black material having the same optical density as the black matrix, as disclosed in PUPA 63-128302, this area is perceived as a black defect. Moreover, it may be impossible to carry out the repair with a photosensitive Negative resin containing a pigment for each of the different specified colors, by irradiation from the side of the transparent substrate, since the tiny areas must be coated separately with a certain thickness. It may be possible by matching with photomasks, but the advantage of this may be very small, since a number of photoprocesses would be required corresponding to the number of defective colors.

Since there is no limitation to eight-color displays with the structure of a gradated red, green, and blue display, the defect becomes more and more noticeable with higher resolution, because the difference between luminance and surrounding pixels becomes larger and the human eye is more sensitive to brightness than to color itself. A pixel with a collection of properly colored pixels displays red, green, blue, or midtones of each color, as well as black, but the defective area displays only white or black. In both cases, the brightness of the defective area is higher than the brightness of the areas where colored pixels are formed, and it is necessary to reduce the transmittance by a repair material. If the brightness is reduced, the defect is harder to detect. The defect is also harder to see when a material of an achromatic color or gray color is used, since the color temperature of this material is equal to the color temperature of white obtained by the additive process of the light emerging from the properly formed pixels of red, green, and blue colors. An achromatic color material is perceived as a black defect in a white display when its transmittance is 30% or less, and it appears white in a color display when its transmittance is 60% or more. When the aperture ratio is about 50%, the optimal transmittance is 30-60%.

A suitable photosensitive negative resin for filling the defective area 13, which extends over several adjacent pixels different color is a radical polymerization photosensitive resin described in PUPA 1-152449 which comprises a polyfunctional acrylic ester monomer, a trihalomethyltriazine type photopolymerization initiator and an acrylic acid/acrylic ester copolymer.

Submicroscopic particles of the achromatic color pigment are finely dispersed in the photosensitive resin. Suitable achromatic color pigments include at least either carbon black or titanium carbon, and if necessary, a color temperature correcting pigment is also added. The color temperature correcting pigment is finely dispersed in submicroscopic particles like the achromatic color pigment. Red, green, blue, yellow and violet pigments are used as needed.

Figure 9 shows the steps of the process for correcting an error extending across pixels of different colors, according to the preferred embodiment. Figure 9 (a) shows a color filter having an error region 13 extending across the adjacent pixels, the red pixel 1R and the green pixel 1G. As shown in Figure 9 (b), a negative photosensitive resin 15 colored in gray or an achromatic color with a pigment is applied to the colored pixels 1B, 1R and 1G and then exposed to light from the transparent substrate side through the colored pixels 1B, 1R and 1G. (Here, these colored pixels serve as photomasks.) The photosensitive resin 15 is then developed. After that, only the negative photosensitive resin 15 remains which has received light through the defective area 13, as shown in Figure 9 (c). The black matrix 2 has a light-shielding function and therefore functions as a photomask. In this way, the negative photosensitive resin does not remain on this part.

What follows is a discussion of two specific implementations of the preferred embodiment described above:

example 1

On a transparent substrate 4 having a black matrix 2 formed thereon by using chromium, COLOR MOSAIC CRY, CGY and CBV manufactured by Fuji-Hant Electronics Technology, Ltd., which are red, green and blue pigments each dispersed in a negative photosensitive resin, were successively coated. Then, the MOSAIC pigments were exposed, developed and baked to produce a color filter. In order to correct a defect 3 in a red pixel 1R of the color filter, CRY was applied thereon by spin coating, exposed with a high-voltage mercury vapor lamp through the colored pixels from the side of the transparent substrate 4 and developed with a specific developing solution. The exposure energy was set to 5 mJ/cm2 because exposure with an energy of more than 5 mJ/cm2 caused polymerization of the photosensitive repair resin even in the correctly prepared red pixel 1R. Under this condition, only the photosensitive resin in the defective area was polymerized, and the defective area 3 could thus be filled with the repair material 5. To form a liquid crystal cell, a transparent ITO electrode was formed by spattering the color filter, and the color filter with the ITO electrode was combined with a TFT substrate. When the display operation was performed using the liquid crystal cell, the defective area could not be identified.

Example 2

On a transparent substrate 4 having a black matrix 2 formed thereon by using chromium, COLOR MOSAIC CRY, CGY and CBV manufactured by Fuji-Hant Electronics Technology, Ltd. were successively coated to produce a color filter through exposure, development and post-baking processes. In order to correct an error thereby generated, which extended over three adjacent pixels colored red, green and blue, respectively, black pigment (carbon black), blue pigment (phthalocyanine blue) and violet pigment (quinacridone red) were mixed, finely dispersed in the photosensitive negative resin solution and applied to the filter. These pigments were added in such a way that the light transmittance was 40%, while the film strength was the same as that of the colored pixels, and the color temperature (9000 K) was the same as the white color resulting from the additive color mixture of red, green and blue. By exposing the resin to an energy of 5 mJ/cm² from the mercury vapor high voltage lamp from the transparent side of the substrate 4 through the colored pixels and by development, only the defective area 13 was filled. By combining the corrected filter with a transparent ITO electrode and a TFT substrate, a liquid crystal cell was prepared, and a display operation was performed using this liquid crystal cell. During the display, the defect, which had looked like a sparkling star before the repair, was almost undetectable.

Figure 10 shows an example of a liquid crystal display with a color filter corrected by the method shown in Figure 1. A nematic liquid crystal layer 50 is inserted between a color filter substrate 100 and a TFT substrate 200. The color filter substrate comprises, in addition to the transparent glass substrate 4 shown in Figure 4: a polarizing plate 8;

red, green and blue pixels 1R, 1G and 1B;

a black matrix 2;

a photosensitive negative resin 5 with red pigment that is filled into the defective area;

a top coat layer 23;

a common ITO electrode 22 formed on the entire surface; and

a liquid crystal alignment film 24 made of, for example, polyimide and formed on the electrode 22.

The TFT substrate 200 is composed of a transparent glass substrate 40, a polarizing plate 9, a gate electrode 30G, a gate insulating film 30I, an a-Si30A, an n+ aSi30N, an ITO pixel electrode 30S, a source-drain electrode 30D, a passivation layer 30P, and a liquid crystal alignment film 32.

In Figure 10, an ITO electrode is provided on the color filter, but as described in PUPA 63-298304, the color filter may also be provided on the ITO electrode.

It will be apparent to those skilled in the art that it is possible to integrate the color filter corrected by the method shown in Figure 9 into a liquid crystal display as shown in Figure 10.

The repair method of the preferred embodiment can significantly improve the display quality when errors occur in the preparation process of the color filter. In addition, according to the preferred embodiment, a desired area can be easily corrected because the repair is performed by self-contained flush filling using the color filter as a photomask.

Claims (6)

1. Method for correcting errors (3) in a color filter containing colored pixels (1B, 1R, 1G), wherein the colored pixels are formed from a photosensitive negative resin containing a pigment, wherein the error or errors only affect pixels of a certain color and wherein the method comprises the steps: for applying a photosensitive, negative repair resin (5) in which a pigment is distributed that has the same color as the colored pixels with the defect, to the colored pixels (1B, 1R, 1G) that have the defect (3); for exposing the applied repair resin (5) with light (6) through the colored pixels (1B, 1R, 1G) which have the defect (3), wherein the light (6) has a wavelength at which the repair resin reacts, but at which the light transmittance of the colored pixels is low, so that the repair resin only reacts in the defective area (3); and to develop the exposed repair resin, leaving only the area of the repair resin that reacted. 2. A method for correcting defects (13) in a color filter having colored pixels (1B, 1R, 1G), wherein the colored pixels are formed from a photosensitive negative resin containing a pigment, wherein each defect extends over several pixels of different colors, and wherein the method comprises the steps of: for applying a photosensitive negative repair resin (15) colored gray with a pigment to the plurality of colored pixels (1B, 1R, 1G) having the defect (13); for exposing the applied repair resin (15) with light (6) through the plurality of colored pixels (1B, 1R, 1G) having the defect (13), wherein the light has a wavelength at which the repair resin reacts, but at which the light transmittance of the colored pixels is low, so that the repair resin only reacts in the defective area (13); and to develop the exposed repair resin, leaving only the area of the repair resin that reacted. 3. A process according to claim 2, wherein the pigment contains at least either carbon black or titanium carbon. 4. A process according to claim 1, wherein the pigment comprises one of the following: (a) at least one pigment of the anthraquinone type and of the perylene type mixed with a yellow pigment of the isomdoline type or a yellow pigment of the disazo type; or (b) a halogenated pigment of the phthalocyanine type with a yellow pigment of the disazo type or a yellow pigment of the isoindoline type; or (c) a phthalocyanine type pigment mixed with a violet dioxazine type pigment; wherein the pigments in (a) are combined to form a red pigment, the pigments in (b) are combined, to form a green pigment and the pigments in (c) are combined to form a blue pigment. 5. A method according to any one of the preceding claims, in which the photosensitive negative repair resin (5; 15) is a resin of the radical polymerization type. 6. A liquid crystal display device comprising a liquid crystal layer (50) disposed between a pair of transparent substrates (100, 200) and a color filter containing colored pixels (1G, 1R, 1B), wherein defective pixels in the filter have been repaired by a method according to any one of claims 2, 3 or 5 so that the defective areas (13) are filled with a negative photosensitive resin of gray color.